Atheists often protest that their critics are more likely to criticise the tone of their arguments than their substance. Accusing someone of being aggressive, nasty or shrill can be a neat way of avoiding the meat of the matter while also appearing to occupy the moral high ground. That's true, but tone does matter, and it's often more connected with substance than it might seem.

"Tone" actually crops up in two guises in this debate. It not only refers to the mode of argumentation but also to the alleged way in which many atheists are "tone deaf" to religion. This second sense is the more important one, and it illuminates the importance of the first. But what does it mean?

Someone who is tone deaf is congenitally unable to distinguish between musical notes and so unable to fully appreciate music. Metaphorical tone deafness is when people are unable to discern what is of value in something. I think I'm tone deaf to poetry, for instance. Despite having studied it into a second year of university, most of it just leaves me cold. Recognising that I just don't seem to "get" what people enjoy about it, I mostly don't say much about it. In such cases, tone deafness might be down to an inherited deficiency or it may be the result of pure ignorance.

But sometimes people are tone deaf and they don't shut up. Take pop and rock music, for example. Many people just don't get it, but it doesn't stop them going on about how it is repetitive, banal, simplistic and so on. They just can't accept that it may have merits they can't discern and that sometimes it is the very things they despise that are essential: think about how repetition is so important to the groove of great funk.

People who are tone deaf about religion are, I think, like people who not only don't get rock music, but are convinced that its value lies entirely in its lyrics. Quite rightly, they might listen to a Deep Purple track such as Highway Star and find lines such as "Nobody gonna take my car, I'm gonna race it to the ground" laughably crass. But then, quite wrongly, they reject the whole track as silly, failing to notice the melodies, harmonies, virtuoso musicianship, musical textures and so on. They might also miss the fact that the melodic and percussive qualities of lyrics often matter more than their semantic content. When Gene Vincent sang "Be-Bop-A-Lula, she's my baby", he knew the sound mattered much more than the meaning.

To make this analogy fair we have to acknowledge one important fact: many religious believers are like Deep Purple fans labouring under the illusion that the lyrics of Highway Star are profoundly meaningful. So atheists who complain they are no such thing are onto something. What makes them tone deaf, however, is that they mistake this something for everything, or at least everything that matters.

I think it is because of this tone deafness that the other problem of tone arises. If you really can't see beyond Highway Star's lyrics, then it's almost inevitable that you're going to come across as arrogant and dismissive when you criticise it. Likewise, if you think that belief in an immaterial father figure is the be-all and end-all of religion, there's no polite way of telling someone you think all that they hold dear is utter nonsense.

That's also why, in this case, to say that an abrasive tone is not constructive is to say more than something about a person's manner of speech. It's not constructive because it is rooted in a one-dimensional understanding of the phenomenon under discussion. Atheistic tone-deafness misses many of the things I've talked about in this series, such as placing mystery at the heart of life, and living with the aid of beneficial rituals and practices. The abrasiveness is not some kind of independent, wilful rudeness that could be smoothed over while keeping the message intact. We talk about people who are rude as being ignorant and more often than not, when someone comes over as too hostile to religion, ignorance is at the root of it, not simply an absence of good manners.

As I've said, this doesn't mean that the charge of ignorance should stick when the attack is on the "lyrics" of the medieval, literal beliefs that still plague much religion. But because so many attacks on religion are tone deaf, it's become easy for the more tuned-in criticisms to be lumped in with them. We atheists parade our inability to "get it" so loudly and often that people assume we are all tone deaf even on the occasions when we hear all too well.

So tone does matter, I'm afraid, and not just because it's good to be nice. Getting the tone right shows you have heard correctly; getting it wrong that you're either incapable of listening properly or unwilling to try to do so.